In a gas turbine, multi-can combustors communicate with each other acoustically due to connections between various cans. Large pressure oscillations, also known as combustion dynamics, result when the heat release fluctuations in the combustors are coupled with the acoustic tones of each of the combustors. In some instances, the acoustic tones of one combustor can is in phase with an adjacent combustor can, while other tones are out of phase with the adjacent combustor can.
In-phase tones are particularly a concern because of their ability to excite turbine blades disposed downstream from the combustor cans. For example, the in-phase tones may coincide with the natural frequency of the blades, thereby impacting the mechanical life of the blades. The in-phase tones are particularly of concern when instabilities between the adjacent cans are coherent (i.e., there is a strong relationship in the frequency and the amplitude of the instability from one can to the next can). Such coherent in-phase tones can excite the turbine blades and lead to durability issues, thereby limiting the operability of the gas turbine.
Current solutions to control in-phase coherent tones include ensuring that the in-phase coherent tones near the turbine blade natural frequency are of much smaller amplitude compared to the typical design practice limits. However, this approach means that the operability limits of the gas turbine could be diminished by the in-phase coherent tones. Another current approach includes changing combustor fuel splits to either shift the combustor instability frequency away from the turbine blade natural frequency or to lower the amplitude. Another solution to control in-phase coherent tones includes increasing or decreasing the overall length of the combustor. However, this solution affects emissions performance and other dynamics frequencies and is not a viable solution for existing gas turbines already in the field. Accordingly, an improved system for controlling in-phase coherent tones within the combustors of a gas turbine would be useful.